1. Field of the Invention
This invention relates to a device for sorting and storing sheets fed from an image forming device such as a copying machine, and more particularly to a sheet sorting device having sheet storing trays each incorporating therein sheet-empty detecting means and sheet-full detecting means in a rational manner.
2. Description of the Prior Art
An image forming device such as a copying machine, printer, facsimile and various type of printing machines is often used with a sheet sorting device for automatically sorting or distributing sheets successively fed from the image forming device to produce sheaves of sheets. The sheet sorting device is ordinarily attached to the side of the image forming device and provided with a plurality of sheet storing trays closely superposed vertically over one another, so that the sheets discharged from the image forming device are sent into the trays in order.
The sheet sorting device of this kind generally necessitates one or more sheet sensors for detecting a sheet or sheets on the tray and checking whether or not the tray is filled with sheets.
One example of a prior art sheet sorting device is disclosed as a paper discharge device in Japanese Patent Application Public Disclosure No. HEI 2-310255(A). As schematically illustrated in FIG. 1A and FIG. 1B, this conventional sheet sorting device is also provided with multistage trays 1a,1b . . . vertically arranged, each having a sheet sensor 2 for detecting a sheet S or sheets Sb introduced from an image forming device into a sheet storing space Rs defined on the tray through sheet transporting means 3.
The sheet sensor 2 comprises a substantially L-shaped sheet detecting lever 2a supported on the tray rotatably about an axis a1, an actuating member 2b rotatable in concert with the lever 2a, and a pair of sheet-empty switch Sw1 and sheet-full switch Sw2, which switches execute switching actions in accordance with the rotation of the actuating member 2b.
For example, when no sheet exists on the lower tray 1b under the tray 1a having the subject lever 2a, the sheet detecting lever 2a on the upper tray 1a falls into an opening formed in the lower tray 1b, as indicated by the solid line in FIG. 1A, to keep the switches Sw1 and Sw2 in their OFF state. When one or more sheets are fed onto the tray 1b, the sheet detecting lever 2a is raised on the tray, as indicated by the solid line in FIG. 1B, to bring the sheet-empty switch Sw1 to its ON state, thus recognizing that one or more sheets exist on the tray.
When the lower tray 1b is filled with the sheets Sb, the lever 2a is raised to its upper limit position as indicated by the dot-dash line in FIG. 1B, consequently to bring the sheet-full switch Sw2 to its ON state. As a result the sheet-full state in which the lower tray becomes full of sheets can be realized by using the sheet-full switch Sw2 mounted on the upper tray 1a.
Thus, the sheet sensor 2 mounted on the specified tray in the conventional sheet sorting device serves to check as to whether any sheet exists on the specified tray and detect the sheet storage limit of the lower tray.
As the sheet detecting lever 2a of the sheet sensor 27 in the conventional device as noted above extends from the upper tray to the lower tray across the sheet storing space Rs, it cannot be made small in size is long as the sheet storing space Rs defined between the upper and lower trays is not narrowed, resulting in a large overall size of the sheet detecting system in the prior art device. In addition to the disadvantage, the free end arm of the L-shaped lever 2a cannot be made long, because the tip of the free end arm collides with the lowermost of the sheets stacked on the tray when the sheets on the tray is increased to move the lever 2a upward. As a result, in the event that a sheaf of sheets, which is once taken out of the sheet storing space Rs, is again inserted intentionally or accidentally into the sheet storing space Rs as indicated by the dotted arrow in FIG. 1B, there is a disadvantageous possibility of causing the sheets to be caught by the lever, or breaking the lever.
The latest sheet sorting device has a tendency to increase the number of the trays for heightening the efficiency of handling the sheets, but inversely, it is desired to be made compact and simple in structure. However, the conventional sheet sorting device could not be made small due to the sheet sensing system which is difficult to miniaturize by the reasons mentioned above.
Furthermore, there is a necessity of detaching one or more trays from the sheet sorting device in use. However, if any tray is detached, the sheets fed onto the lower tray do not reach the sheet detecting lever 2a mounted on the upper tray, resulting in malfunction of the sheet sensing system. That is, the conventional sheet sorting device cannot be used practically in the state of taking the tray out.
In addition, in the conventional sheet sorting device as mentioned above, electric elements including the switches Sw1 and Sw2 are secured on each tray along with the sheet detecting lever 2a and actuating member 2b. Therefore, when the tray is detached from and attached to the sheet sorting device, the work of establishing an electrical connection a disconnection between the electric elements mounted in the tray and the sheet sorting device is required. This turns out to be a very troublesome chore.